Dependence of Rotating Frame Relaxation Rates on Frequency Offset: Spin-Lock Versus Adiabatic Rotation

Silvia Mangia¹, Timo Liimatainen¹, Michael Garwood¹, Shalom Michaeli¹

In the present work we investigate the frequency offset dependency of the rotating frame longitudinal, R_1ρ, and transverse, R_2ρ, relaxation rate constants during continuous-wave spin-lock irradiation and during hyperbolic secant adiabatic full passage pulses. We demonstrate, both theoretically and experimentally, that R_1ρ and R_2ρ induced by dipolar interactions and anisochronous exchange during hyperbolic secant pulses are minimally dependent on the frequency offsetwithin the bandwidth of the pulse, as opposite to continuous-wave irradiation. This is a unique advantage for MRS applications in vivo, because it allows "one shot" data acquisition over a wide range of chemical shift.